Materials which emit light when an electric current is passed through them are known as electroluminescent materials and are well known and used in a wide range of display applications. Liquid crystal devices and devices which are based on inorganic semiconductor systems are widely used, however these suffer from the disadvantages of high energy consumption, high cost of manufacture, low quantum efficiency and the inability to make flat panel displays.
Organic polymers have been proposed as useful in electroluminescent devices, but it is not possible to obtain pure colours, they are expensive to make and have a relatively low efficiency.
Another compound which has been proposed is aluminum quinolate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
Patent application WO98/58037, which is incorporated herein by reference, describes a range of lanthanide complexes which can be used in electroluminescent devices which have improved properties and give better results. Patent Applications PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028, PCT/GB00/00268, which are incorporated herein by reference, describe electroluminescent complexes, structures and devices using rare earth chelates.
Hitherto electroluminescent metal complexes have been based on a rare earth, transition metal, lanthanide or an actinide or have been quinolates such as aluminium quinolate.